The present invention generally relates to an internal combustion engine (hereinbelow, referred to as an "engine") and more particularly, to a fuel supply arrangement for the engine.
Conventionally, in fuel supply arrangements for engines, it has been generally so arranged that a proper amount of fuel is supplied to the engines in accordance with amount of intake air so as to operate the engines efficiently. For example, in carburetors of the known engines, supply amount of the fuel to the engines is controlled by negative pressure of a venturi of an intake passage. On the other hand, in fuel injection devices of the known engines, the amount of intake air is detected by an air flow sensor such that injected amount of the fuel to the engines is controlled in accordance with output of the air flow sensor. However, in the case where the supply amount of the fuel to the engines is controlled by only the negative pressure of the venturi, the known carburetors have such a disadvantage that since the negative pressure of the venturi varies in accordance with flow velocity of the intake air as a parameter, an air-fuel ratio of the air-fuel mixture deviates from a preset value when a density of the intake air varies upon change of temperature of the intake air. On the other hand, in the case where the supply amount of the fuel to the engines is controlled in accordance with only the output of the air flow sensor, the known fuel injection devices have such an inconvenience that since a Karman vortex type, speed density type or vane type sensor arranged to detect volume flow rate of the intake air is usually employed for the air flow sensor, an air fuel ratio of the air-fuel mixture deviates from a preset value when a density of the intake air varies upon change of temperature of the intake air.
In order to eliminate such a drawback of the prior art fuel supply arrangements, there has been proposed a fuel supply arrangement in which an air temperature sensor for detecting temperature of intake air is provided in the course of an intake passage such that supply amount of the fuel to the engine is correctively controlled in accordance with output of the air temperature sensor as disclosed, for example, in Japanese Patent Laid-Open Publication No. 51922/1982 (Tokkaisho No. 57-51922). However, this known fuel supply arrangement is also disadvantageous in that output of the engine drops or the engine stops at the time of starting the engine in a hot state or at the time of acceleration of the engine.
In order to obviate the drawbacks of the above described known fuel supply arrangement, i.e. drop of the output of engine or stop of the engine at the time of starting the engine in the hot state or at the time of acceleration of the engine, the present inventors made thorough study and have discovered causes of the drop of the output of the engine or the stop of the engine, which will be described with reference to FIG. 1, hereinbelow. FIG. 1 illustrates changes with time of temperature a of the intake air in the intake passage, output b of the air temperature sensor for detecting the temperature a of the intake air, temperature c of cooling water of the engine and atmospheric temperature d. It will be readily seen from FIG. 1 that when the engine is started in a cold state, the air temperature sensor for detecting the temperature a (one-dot chain line) of the intake air detects the temperature a of the intake air without time lag as shown by the solid line b. Meanwhile, as shown by the solid line c, the temperature c of the cooling water of the engine rises immediately upon starting of the engine and reaches a constant value of about 80.degree. C. Once the engine is stopped, the temperature c of the cooling water gradually drops from about 80.degree. C. At this time, since the intake air in the intake passage is heated by the high-temperature cooling water of the engine, the temperature a of the intake air rises sharply from about 30.degree. C., so that the sensor itself in contact with the high-temperature intake air is heated to a high temperature.
When the engine is started in such a state, i.e. in the hot state, low-temperature atmosphere shown by the broken line d is introduced into the intake passage, so that the temperature a of the intake air immediately drops to the previous temperature of about 30.degree. C. Meanwhile, since the air temperature sensor is heated to the high temperature by the intake air at the time of stop of the engine as described above, the air temperature sensor detects the temperature a of the intake air with time lag and therefore, yields an output b corresponding to a temperature higher than the actual temperature a of the intake air. Accordingly, when the supply amount of the fuel to the engine is correctively controlled at this time in accordance with the output of the air temperature sensor, the corrective control of the supply amount of the fuel to the engine is exceedingly effected such that the supply amount of the fuel to the engine is decreased, so that the air-fuel mixture becomes excessively lean and thus, the output of the engine drops or the engine stops. Namely, the present inventors have found that the drop of the output of the engine or the stop of the engine takes place due to sudden increase of the supply amount of the intake air to the engine and time lag of detection of the air temperature sensor, which time lag of detection of the air temperature sensor is caused by the sudden increase of the supply amount of the intake air to the engine.